This invention relates to swimming pool cleaning devices that operate automatically to move over the surface to be cleaned when water is induced to flow through the device by the suction created by conventional swimming pool filtration equipment. In these devices water flow in a flow passage through the device is intermittently interrupted by a valve mechanism in the passage with the result that the device moves step-wise in random fashion over the pool surfaces. This allows the surfaces to be cleaned by water flowing over such surfaces into and through the device to the filter unit.
Among the various valving arrangements that have been proposed for such cleaning devices U.S. Pat. No. 4,769,867 describes a valve in the form of a pair of "jaw-like" members biased to an open position by the inherent elasticity of the plastic material forming a portion or all of the valve. The mode of operation is as follows. When suction is applied to the flow passage water flows through the passage and this reduces the pressure at the internal surfaces of the valve. When the flow velocity reaches a critical value, the valve closes due to the differentially higher pressure on the external surfaces of the valve which overcomes the biasing force maintaining the "jaws" at the open position.
While the described valve could have potential advantages of simplicity, relatively compact size and reduced susceptibility to plugging by debris, it has inherent limitations which render it unsatisfactory as it is incapable of achieving the sustained operation required for typical applications in which the cleaner is operated on a daily cycle, usually for daily periods of up to 18 hours or higher. Over a period of a year of such sustained operation may require up to fifty million or more beats or cycles of the valve.
Specifically, it has been found that in operation over time elastomeric material employed to bias the valve to the open position is inherently subject to creep and gradually looses its "memory" such that the "jaws" do not return completely to the open position. As this memory loss or creep progresses the valve begins to cycle more rapidly, with consequent undesirable loss of flow rate, and finally the valve ceases to function entirely.
The memory loss defect has been partially overcome by application of an auxiliary, low creep biasing means to maintain the valve open during periods of non-use, thus permitting at least partial restoration of the memory of the elastomeric material. Nevertheless, over time, permanent deformation will still take place which increases maintenance requirements eventually requires replacement of the valve.
Equally important, construction of a valve of the described empirical design that will actually operate, much less operate reliably under field conditions, is, at best, a haphazard proposition.
Additionally, the "jaw-type" valves described are susceptible to fouling by debris becoming caught at the corners (side margins) of the mouth opening. When the jaws attempt to close on the debris at the corners, they are held at a partially open position and are then unable to either reopen or close completely. Consequently, the cleaner will cease to function until it is shut off, the debris removed and then restarted.